The invention relates to color film and in particular to a method of making a random color filter array film.
The great majority of color photographs today are taken using chromogenic color film, in which color-forming couplers, which may be incorporated in the film or present in the processing solution, form cyan, magenta and yellow dyes by reaction with oxidized developing agent which is formed where silver halide is developed in an imagewise pattern. Such films require a development process which is carefully controlled in respect of time and temperature, which is usually followed by a silver bleaching and a fixing step, and the whole process typically takes several minutes and needs complex equipment.
Color photography by exposing a black-and-white photographic emulsion through a color filter array which is an integral part of the film or plate on which the photographic emulsion is coated, has long been known to offer certain advantages of simplicity or convenience in color photography. Thus the Autochrome process, disclosed by the Lumiere brothers in 1906 (U.S. Pat. No. 822,532) exposed the emulsion through a randomly disposed layer of red, green and blue-colored potato starch grains, and the emulsion was reversal processed to give a positive image of the scene which appeared colored when viewed by light transmitted through the plate. The process allowed the formation of a colored photograph without the chemical complexity of later photographic methods.
The Dufaycolor process (initially the Dioptichrome plate, L.Dufay, 1909) used a regular array of red, green and blue dyed patches and lines printed on a gelatin layer in conjunction with a reversal-processed black-and-white emulsion system, which similarly gave a colored image of the scene when viewed by transmitted light.
Polavision (Edwin Land and the Polaroid Corporation, 1977) was a color movie system employing a rapid and convenient reversal processing method on a black-and-white emulsion system coated above an array of red, green and blue stripes, which gave a colored projected image. It was marketed as a still color transparency system called Polachrome in 1983.
These methods suffered a number of disadvantages. The images were best viewed by passing light through the processed film or plate, and the image quality was not sufficient to allow high quality prints to be prepared from them, due to the coarse nature of the Autochrome and Dufaycolor filter arrays, and the coarse nature of the positive silver image in the Polavision and Polacolor systems. The regular array patterns were complicated and expensive to manufacture. In addition, the films which used regular or repeating filter arrays were susceptible to color aliasing when used to photograph scenes with geometrically repeating features.
U.S. Pat. No. 4,971,869 discloses a film with a regular repeating filter array which claims to be less susceptible to aliasing problems. The film disclosed comprises a panchromatic photographic emulsion and a repetitive pattern of a unit of adjacent colored cells wherein at least one of the cells is of a subtractive primary color (e.g. yellow, magenta or cyan) or of a pastel color. Scene information can be extracted from the developed film by opto-electronic scanning methods.
European Patent Application 935 168 discloses a light sensitive material comprising a transparent support having thereon a silver halide emulsion layer and a randomly arranged color filter layer comprising colored resin particles. Also disclosed is exposing, processing and elecro-optically scanning the resultant image in such a film and reconstructing the image by digital image processing.
Color photographic films which comprise a color filter array and a single image recording layer or layer pack have the advantage of rapid and convenient photographic processing, as the single image recording layer or layer pack can be processed rapidly without the problem of mismatching different color records if small variations occur in the process. A small change in extent of development for example will affect all color records equally. Exceptionally rapid processing is possible using simple negative black-and-white development, and if suitable developing agents are included in the coating, the photographic response can be remarkably robust or tolerant towards inadvertent variations in processing time or temperature. Developing agents suitable for including in the coating, and a preferred way of incorporating them, are disclosed in U.S. 5,804,359.
It is desirable that the method of manufacturing the color filter array be of comparatively low cost. Known methods of making regular filter arrays, such as those used for Dufaycolor or Polachrome films, are complex and costly, involving several sequential applications of materials to the film. Known methods of making random filter arrays, such as those used for Autochrome film and that described in EP 935 168 also involve complex operations, including separating and grading or sizing the colored particles of starch or resin respectively, dispersing them in a coating medium, coating and drying and then calendaring the coated layer to flatten the particles.
It is an object of the invention to provide a method of making a color filter array film which is simpler and of comparatively low cost as compared to methods known in the prior art.
According to the invention there is provided a method of making a random color filter array comprising the steps of:
dispersing in an aqueous medium a water immiscible oily liquid having dyes and/or pigment particles dissolved and/or dispersed therein to form colored droplets,
mixing the resulting dispersion with one or more other dispersions of different colors in a continuous aqueous phase having a film forming polymer dissolved therein and
coating the resulting mixture onto a support layer.
Preferably any pigment particles dispersed within the water immiscible oily liquid have a mean length of less than 0.5 micrometers.
The method of the invention uses existing photographic manufacturing methods such as oil-in-water dispersion and photographic coating. Thus no new equipment is required. Furthermore there is no need to separate or isolate the color elements. Little or no volatile organic solvents need to be evaporated or recovered and the only drying step is the normal drying of a coated photographic film. No calendaring step needed as the fluid filter elements become flatter as the coating dries.
The method of the invention also allows convenient manufacture of films having a preferred film structure in which the CFA is located between the emulsion layers and the top coated surface of the film, that is located further from the support than the emulsion layers. This film structure is preferred because it allows the film to be exposed in the camera with the support towards the back of the camera and the emulsion side toward the lens, which is the orientation for which films and cameras are normally designed. Such a film structure is preferred in the case of Advanced Photographic System films because the magnetic recording layer functions most effectively when coated on the back of the support and has to be in contact with the magnetic heads in the back of the camera. The filter array preparation methods of the prior art would entail complex operations on top of an already-coated emulsion layer, which would need to be done under safelight conditions and would risk harming the very sensitive coated emulsion layers for instance by causing fog or desensitization. Heat calendaring operations, as used in the method described in EP 935 168 could very probably cause heat and pressure fog in the already-coated emulsion layer(s).
In the case of digital image capture devices such as digital cameras and scanners, the method of the invention provides a low cost means of manufacturing color filter arrays, and the random nature of the array will give reduced color fringing at edges and with fine geometric structures in the scene, relative to a regular color array.
Reference is made to related commonly owned co-pending applications entitled Film with Random Color Filter Array, U.S. Ser. No. 09/808,873, and Random Color Filter Array, U.S. Ser. No. 09/810,787, both filed concurrently herewith, the entire contents of which are incorporated herein.